Study on Fit Clearance and Motion Performance of All-Metal PDM

The stator and rotor of the all-metal positive displacement motors (PDM) adopt the clearance fit. The size of the clearance will have a significant impact on the working characteristics, which is manifested in the leakage. In order to further study the leakage mode and motion characteristics of the all-metal PDM under clearance fit, several mathematical models of different clearance were established, and the single-phase fluid leakage model of the all-metal PDM based on different flow patterns was established by applying the clearance flow principle, which realized the quantitative calculation of the leakage in the metal motor, and the displacement characteristic curve of the all-metal PDM was drawn. The results show that the leakage and pressure drop of the all-metal PDM mainly depend on the design of motor line type, the fitting clearance of stator and rotor, the displacement and the viscosity of drilling fluid. Among them, fit clearance and drilling fluid viscosity have great influence. The larger the clearance value, the more serious the leakage; The higher the viscosity of the drilling fluid, the lower the loss, but there is a threshold. The all-metal PDM is more suitable for the formation with large temperature gradient changes. In practical application, the kinematic performance can be guaranteed by reasonable selection of clearance and medium viscosity.